A nasty dispute involving Native American tribes and gambling is about to get a little bit nastier.

Rep. Raul Grijalva (D-Ariz.), a member of the House Natural Resources Committee, has sent a letter to the top lawmakers on the panel demanding that a lobbyist for the powerful firm of Akin Gump Strauss Hauer & Feld publicly apologize for a tweet slamming a Native American chief that Grijalva has known since high school.

The spat grew out of a big-money fight over a planned tribal casino in the Phoenix area — Grijalva represents a large district south and west of the city — and the millions of dollars it could rake in annually. Akin Gump and its lobbyist, James Meggesto, represent the Gila River Indian tribe, which already operates several Arizona casinos. The Gila River and Salt River Pima-Maricopa tribes — another casino operator — have joined with Arizona officials and several GOP congressmen in trying to prevent a third tribe, the Tohono O’odham Nation, from opening its casino close to downtown Phoenix.

Grijalva, a close friend of Ned Norris, the chairman of the Tohono O’odham tribe, is strongly opposed to a bill offered by Rep. Trent Franks (R-Ariz.) that would bar the new casino from being opened. Franks introduced a similar bill in the House during the last Congress. The measure was adopted by the House but later died in the Senate.

The long-running and costly dispute has not only spilled over onto Capitol Hill but into the federal courts. Akin Gump has been paid hundreds of thousands of dollars by the Gila River tribe for its lobbying work, including nearly $1.2 million this year alone, lobbying disclosure records show. The Tohono O’odham tribes has also spent big money on its own hired guns.

During a May 16 hearing in a Natural Resources subcommittee, Norris testified in opposition to the latest version of the Franks bill.

As Norris was testifying, Meggesto sent out this tweet: “Resisting urge to tweet about a pair of high school buddies, one is lying under oath and the other is on the dais enabling him #Indianlands.”

Meggesto’s tweet, without mentioning them by name, was clearly referring to Grijalva and Norris.

Grijalva was outraged by Meggesto’s tweet — since deleted — and has sought a public apology, so far to no avail.

Now Grijalva — whose leadership PAC received a $5,000 contribution from the Tohono O’odham tribe in August 2012 — wants Reps. Doc Hastings (R-Wash.) and Peter DeFazio (D-Ore.), the chairman and ranking member of Natural Resources, to act.

“I take the accusations of perjury very seriously, [and] I formally ask the committee to request that Mr. Meggesto or his employer present evidence of false statements made under oath. Absent evidence or proof, I request a formal apology to Chairman Norris,” Grijalva said in his letter to Hastings and DeFazio. “Organizations with business before Congress must conduct themselves in a professional manner and understand that slander — no matter the means of communication — will not be tolerated.”

Meggesto did not respond to requests for comment.

Benjamin Harris, a spokesman for Akin Gump, said the firm was looking into the issue. “Mr. Meggesto’s personal tweets are not necessarily reflective of the views of Akin Gump on this or any matter,” Harris said in a statement. “We are aware of the issue raised by Rep. Grijalva today and are reviewing the matter internally.”

It’s not clear that the Natural Resources Committee could sanction Meggesto or Akin Gump, but the matter could prove embarrassing to the prestigious firm.

“As a public figure, what [Meggesto] said, heck, I’m used to it,” Grijalva said. “But on Chairman Norris, if [Meggesto] felt to public accuse him of perjuring himself before a congressional committee, he needs to back it up.”